1. Field of the Invention
The present invention relates to an image development apparatus such as a laser beam printer (hereinafter referred to as LBP) and a photocopying machine, having a cooling device.
2. Description of the Related Art
A typical construction of low-cost LBPs today is shown in FIG. 8. In this construction, a paper feeder section 61, a transfer section 62, a fixing section 63, a process cartridge 64 and the like are closely mounted on a center stay member 60 as printer building members to shorten a recording medium transport path Q, while electronics 65 are arranged together below the center stay member 60 to make the entire construction of the LBP compact.
A fixing unit that constitutes the fixing section 63 adopts, instead of a heating roller method of using a halogen heater, a fixing method which causes a pressure roller 63c to press a heat-resistant film 63b against a flat-plate ceramic heater 63a so that a recording medium P fed into a nip formed between the heat resistant film 63b and the pressure roller 63c is allowed to advance along with the heat resistant film 63b (hereinafter, this method is referred to as SURF fixing method). The SURF fixing method completely switches off the heater when not in use, to save power, and offers many excellent features such as quick start and less-wait-time features.
Since the heater is switched off for durations other than printing operation periods, heat generation from the fixing unit is minimized, and thus a cooling fan for cooling the body of the apparatus, which would be essentially required if a heating roller type fixing unit was employed, is dispensed with. This arrangement substantially contributes to compact design and substantial cost reduction of the apparatus.
However, the conventional fan-less compact LBP thus constructed presents the following disadvantages.
(1) Since the process cartridge 64 is mounted closely to the fixing section 63 to make the entire structure of the printer compact as shown in FIG. 8, the process cartridge 64 is subject to heat emitted from the fixing section 63. Particularly when a large quantity of printing jobs is performed continuously, heating effect is considerable even in the SURF fixing method because the heater remains switched on continuously for a long time. In the course of such heating, the surface temperature of a photoconductive drum as an image bearing body increases, possibly adversely affecting electrostatic image formation on a development section.
If a cleaning container 64a for recycling toner residing on the photoconductive drum is heated after a transfer operation, waste toner in the vicinity of a cleaning blade 64b solidifies and a cleaning operation possibly malfunctions.
(2) When a large quantity of printing jobs is done, heated air builds up within an upper space which accommodates the fixing unit, not only because the fixing heater of the fixing section as a major heat source remains switched on for a long period of time but also because the center stay member 60 separates the upper space and a lower space, respectively, above and below the recording medium transport path Q. As a result, the internal temperature of the apparatus rises.
(3) When a large quantity of printing jobs is performed with no cooling fan employed, the fixing unit that has been heated starts giving off heat at the end of a printing operation. The internal temperature in the cabinet of the printer is expected to rise higher than even at the time of printer stop.